Part of the IALA Buoyage System (International Association of Lighthouse Authorities) the Cardinal Marks are designed to show us the safest water in which to navigate.
The “Cardinal Rule” is to stay on the side of the cardinal that it is telling you i.e. A North Cardinal mark means the safest water is to the NORTH. The cardinal mark may be protecting you from a reef, shipwreck, substantial hazard or separating a shipping channel.
There are 4 cardinal marks and each one has two cones pointing differently to represent each cardinal compass point.
The rule is simple and the real skill when boating is to identify each cardinal so you can steer around it safely by compass or sense of direction.
Whoever designed the system was a clear thinker and here is one simple way to remember the directions.
NORTH points up, SOUTH points down as pictured and if you think about a chart or the Earth, then it makes perfect sense.
EAST and WEST are also easy if you imagine a sunrise or sunset on the horizon, if you were at sea it would be reflected on the water like this: –
Again looking at the diagram, the distinctive colours black and yellow also help identify each cardinal and follows the direction of the cones – the black stripe is in the position pointed to by the cones.
To identify the cardinals at night, the light sequence or code is also logical. Looking at the main diagram and imagining a round clock face and the numbers 12, 3, 6 and 9 positioned on each cardinal you can also remember how they might flash and is a white light generally over a period of 10 seconds. The sequence or code is loosely as follows; East 3x, South 6x plus one long, West 9x, and North a continuous flash.
Like all the theory, it becomes easier to understand when you apply this when you are in a boat, on the water!
The Buoyage System is a basic knowledge requirement of Masters and must be observed for the safe navigation of all vessels.